Process of making castings



May 17,1938.

J. FLAMMANG- El' AL PROCESS OF MAKING CASTINGS FiledQl-v. e, 1955 town ws A e H Patented May 1.7, 1938 UNITED STATESl PaocEss oF MAKING CASTINGS John Flammang and Percy L. Bowser, University City, and Herman Ernst, Pine Lawn, Mo., as-

signors to The Sterling Corporation, St. Louis, Mo., a corporation of Delaware ,l

Application November 6, 1935, Serial No. 48,466

4 Claims.,

This invention pertains to a process for making castings and more particularly to making castings of light metals, such as aluminum, magnesium and their alloys. The process is designed 5 more particularly for casting trunk' pistons for internal combustion engines, but it may be applied to other castings.

In castings having forms whereby certain portions thereof are made massive and contain a rel `1o atively large quantity of metal and other portions thereof are relatively light, so as to contain smaller quantities of metal, when the castings are cooled in the ordinary manner by allowing them tostand `in atmospheric air, the cooling is l5 usually such as to reduce the temperature of the lighter portions of the casting at a more rapid rate than that of the more massive portions. As a consequence of this action, the lighter portions have contracted to their iinal dimensions before the temperature of the more massive portions has dropped to that of the atmosphere. Further cooling of these massive portions, therefore, tends to contract the entire structure and therefore imposes contraction stresses upon those parts which have already attained their nal form.

It has been found that with certain kinds of castings, such as trunk pistons, wherein it is customary, after finishing the outer surface, to partially separate the head from the skirt by a circumferential saw cut, or to split the skirt by a vertical slot or slots after such saw cuts have been made, the skirt portion has bulged to the extent of several thousandths of an inch. Such an eil'ect usually requires that the casting be renished. It may be assumed that this edect is due to the fact that the cooling and contraction ot the piston head, after the skirt portion has attained its nal dimensions, exerts an inwardly directed stress, tending to draw the skirt portion in- 40 wardly, which stress is relieved by separating the head and skirt.

One of the objects of this invention is to provide a method whereby the above outlined dii't iiculties may be overcome.

Another object is to provide a process wherein the cooling of a casting may be so regulated that all parts thereof will contract atY substantially the same rate.

Another object is to provide a process whereby heat may be extracted from certain portions of the casting at a greater rate than at other portions, so that a more uniform cooling may be obtained. f

Further objects will appear-from the following description, taken in connection with the accompanying drawing, illustrating the several steps of a process embodying this invention, in which Figure l is a sectional view of a mold in which apiston castingzis formed: and 4 i Figure 2 is-.afsectional view of the quenching 5 bath.

In accordance with the process of this invention, the casting i is formed in a suitable mold 2 to the-desired form. I'he mold 2 may be of any suitable construction.` In the drawing, the cast- 10 ing of a piston is illustrated. In casting pistons, the molds 2 are usually of metal. Accordingly, when the casting is poured, it receives a prelim- 4inary chill by dissipation of heat to the mold 2.

Piston castings of the kind illustrated are usually made of alloys containing aluminum, copper, magnesium and sometimes other ingredients in suitable proportions. While the casting metal is in the molten stage, these ingredients are probably in solution, one in the other. During the cooling process, particularly if the cooling is at a slow rate, there is a tendency for the different ingredients to become segregated. It is desirable to arrest the segregating action as early 'as possible, as it has a tendency to render the casting soft. By increasing the cooling rate, as by the preliminary chill in the metal mold 2, or by. quenching, as will be explained hereinafter, this segregation is checked and the quality of the iinished casting improved. 3'0

In accordance with the present invention, the casting is preferably allowed to cool for a short period of time in the atmospheric air, after having been removed from the mold. A convenient way of carrying out this process is to set the iinished casting aside, as indicated at A in Figure l, for a short time suilicient to permit the casting to become completely solidiiied and hard enough to withstand-handling with tongs or similar appliances. The casting may be simply removed from the mold and set uponthe molding table, as indicated in Figure 1. By setting the casting head down so as to rest on the spx-ue 3, as shown, it may have contact with the air substantially all over its suriace.` The casting may be allowed to stand thus for a short time, for instance, just long enough to pour another casting. Such an interval may be as short as 15 or 25 seconds. During that time, the casting may 'cool down by a fall of temperature of -100 F. It is desirable to remove the casting to the quenching bath I, shown in Figure 2, when it has attained a temperature of between 850 and 825 F. v When the lcasting has attained the proper temperature, it is removed to the quenching bath l, 55

shown in Figure 2. This may be a water bath provided just below the bevel of the water therein, with a series of transverse supporting rods, such as indicated at 5, adapted to support the castings. Any suitable type of support, such as a grid, may be employed for this purpose. The spaces between theA supporting members are preferably suilcient to'permit the sprue 3 to pass therethrough so that the casting rests upon the piston head, as shown in the drawing. The level of the water in the tank is maintained at a height about equal to that of the inside surface of the piston head. The casings are thus submerged for only a small depth in the quenching bath. The remaining portions of the skirt and also the inside of the piston head are in contact with 'the atmospheric air, so that they continue to cool at substantially the same ate as when in the position A in Figure 1. The submerged portions of the casting, however, are now bathed by the quenching liquid which extracts heat therefrom Yat a more'apid rate than they would cool in air.

.By proper adjustment of the level of the quenching liquid .with reference to the casting, the rate of cooling of the submerged portions may be adjusted so as to be substantially equal to that of the unsubmerged portions. That is to say that all portions of the casting cool at substantially the same rate and, accordingly, shrinkage will be -at the s'ame rate throughout the casting so that cooling stresses are avoided.

It has been found that for piston castings of the type shown, the liquid level is best maintained at about the height of the inside of the piston head. For other forlns of castings, it may be necessary to adjust this level to a somewhat different point, such that the extraction of heat from the submerged portion progresses at such a rate as to bring the temperature down Iat the same rate as that of the unsubmerged portions.

It will be noted that the bath l is of large volume compared with that of the castings. By providing a large quantity of quenching liquid, the bath may be maintained at substantially uniform temperature as the heating effect on the bath due to immersing the castings therein may be labsorbed by the large volume of liquid. The temperature is preferably maintained between 190 F. and the boiling point for the water bath.

'In order to maintain the level of the quenching bath constant, water may be supplied thereto from a suitable source not shown through a regulating valve 6 to a coil 'l within the bath. This coil may be arranged to circle the bath a few times so that the incoming water maybe heated before being delivered at the outlet 8 of the coil.

It will be seen that this invention provides a process whereby the unequal cooling of a piston or similar casting may be compensated for and the cooling stresses virtually entirely eliminated.

While the process has been described as a complete whole, it will be understood that certain individual features or subcombinations thereof may be useful without reference to other features, and the employment of such individual features or subcombinations is contemplated by this invention and within the scope of the appended claims. It is obvious that various changes may be made in the details of procedure, within the scope of the appended claims, without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specific details shown and/or described.

Having thus described the invention, what is claimed is: l

1. The process of making a piston casting having a massive head and a thin skirt, comprising, forming the casting in a mold, removing the casting from the mold after it has solidiiied, and quenching the head portion of the still-hot casting while the skirt portion is permitted to cool gradually.

2. 'Ihe process of making a piston casting hav- I ing a massive head and a thin skirt, comprising, forming the casting in a mold, removing the casting from the mold after it has solidified, permitting preliminarily gradual but only partial cooling of the entire casting after such removal, and thereafter quenching the head portion of the still-hot casting while the skirt portion is permitted to cool gradually.

3. 'I'he process of making a piston casting having a massive head and a thin skirt, comprising, forming the casting in a metal moldv so as to chill the metal, removing the chilled casting from the metal mold after it has solidified, and quenching the head portion of the still-hot casting while the skirt portion is permitted to cool gradually.

4. The process of making a piston casting having a massivehead and a thin skirt, comprising, forming the casting in a mold, removing the casting from the mold after vit has solidiiled, and quenching the head portion of the still-hot casting by dipping the same to a shallow depth into a quenching bath while the skirt portion and the inside of the head are permitted to cool gradually.

JOHN FLAMMANG. PERCY L. BOWSER. HERMAN ERNST. 

